New Machine Build- My New cnc gantry machine.

[siaug18]

Hi all,

I am so excited at the moment.. I have just finished the x and y axis on my gantry cnc.

I checked the accuracy of both axis and was very happy with the results.

x-axis is out by 0.004 inch and the z axis is o.ooo inch

All I have to do now is finish the z axis, but that will have to wait until next weekend.

I tried to upload some video's but it keeps failing.. any ideas

[ger21]

Videos are usually to big to post here. put them on Youtube and give us the link.

[siaug18]

hi, thanks for the advice. links below

x-axis:

YouTube - x-axis accuracy

YouTube - x-axis accuracy

y-axis:

YouTube - y axis accuracy test

YouTube - y axis accuracy test

[joecnc2006]

sounds like your motors are pulsing?

[siaug18]

hi joe ,

What do you mean about pulsing ?


I did some photos this morning to show more details.

[joecnc2006]

In your video's sounds like your motors are pulsing, may be amplified with video sound, but i remember mine did that when i used a 36v 14a psu, regulated, then i built my own with transformer, rectifier and cap, and it eliminated the noise.

Is that three PSU's wired together in the bottom of the controller? The gecko's may not like them. You may want to ask GeckoDrives in an E-mail what their opinion may be on the wired PSU's.

Joe

[siaug18]

Hi Joe,

The supplies are telecomms 47v 9.9A supplies, each gecko has its own supply which has emc mains filters fitted. I can hear the pulsing noise on the video but i don't have any idea what is causing it.

I would build my own supplies but each of my stepper motors needs about 10A at about 45-50v so the supply would be massive and the in-rush current would be a concern . The supplies I am using pull about 19 amps on power up for about 0.4 seconds that is why i have fitted a relay time control so each supply turns on 1 second apart. “ just a 16f84 and 3 240v 20A relays”

Anyway back to the pulsing.. I will have a look on the internet to see if i can figure out what is causing it !
Maybe it resonance ? Maybe i should try to increase the decoupling capacitors ?

If you have any ideas just let me know.

[ger21]

A gecko stepper drive should not need more than about 5 amps each. If you read the info on Gecko's website, it'll tell you that a bipolar parallel stepper will not need more than 2/3 of it's rated current, and most of the time it will use much less. So at most, a single 15 amp supply is all you would need, if you were running 7 amp steppers. If you're steppers are rated at 5 amps or less, a single 10amp supply should be enough.

[Gir]

pull about 19 amps on power up for about 0.4 seconds that is why i have fitted a relay time control so each supply turns on 1 second apart.

You're always going to get a very large current spike when turning on the power supplies due to the capacitors that need charging. To mitigate this you could always put a thermistor before the capacitor bank. A thermistor has very high resistance when it is cold, but as soon as that current starts flowing through it it will heat up very quickly and it's resistance will drop to very little, thus causing a sort of "soft start".

As for 19A, I'm assuming that's off of the primary, which seems to be where it should. Ger is right; those steppers aren't pulling 10A each, possibly not even 10A total. I'd be curious how effective that filter on the PSU is. Can you tell us how big of a capacitor is inside them? If it's anything under 20mF (20,000uF), that could be your problem - they're not filtered enough and you'd be getting some pretty big ripples. That seems to be what John fixed in his. It wasn't the transformer (a transformer's a transformer and will work until it melts/arcs), but the filter network was probably better and could handle the current. The one that didn't work for him probably had too small of a capacitor bank.

Anyway, good luck with that! Your machine looks great!

[siaug18]

The stepper motors I am using are rated at 15A total so 2/3 of that is about 10A, thats why i have no current limiting resistors on the gecko drives.

The power supplies are switch mode supplies.

I did some tinkering last night and replaced the 470uF 63V decoupling capacitors with some 520uF 100V and it seems to have removed the pulsing noise.

[joecnc2006]

Gecko stepper drivers are up to 7amp. from your picture looks like you are using a 7a driver, so depending on your current resister, that is the amps you are putting to the motors not 15amp.

Joe

[samco]

It 'sounds' like my steppers did trying to use turbocnc on a laptop. (Power management/laptop issue). I would get rhythmic ticking from the steppers. Have you run the test program in mach (I am not a mach person.. So others will have to chime in) Cool project.

sam